I see a couple of things. You apparently have several Adobe Acrobat Pro browser plug-ins installed. If any of these are not compatible with Mountain Lion, or Safari, they too can be problematic in normal Safari operation.
Adobe Reader 11.0 (in my case) installs two files into /Library/Internet Plug-Ins:
- AdobePDFViewer.plugin
- AdobePDFViewerNPAPI.plugin
And in the same location, Safari would otherwise use:
Quartz Composer.webplugin
The Adobe Reader 11.0 plug-ins will take priority over the default Quartz Composer web plugin. This is my preference as it offers extended PDF handling.
If you remove both Reader items 1 and 2, then if there are no other Adobe Acrobat plugin conflicts, Safari should resort back to using the Quartz Composer PDF plug-in.
In the Finder sidebar, under DEVICES, the top item should be a small disk drive with your hostname next to it. Double-click that item. Now you have another hard drive symbol that bears the name of the partition you installed OS X on. It might be Macintosh HD. Double-click this icon. Now, double-click Library, and then Internet Plug-Ins.
Select both AdobePDFViewer plugin files. Now, right-button click and move them to the Trash. Since these are system files, you will be prompted for your login password to complete the removal. Empty the Trash.
The next time you run Acrobat Reader 11.0, it will re-install these two PDF plugins. Adobe Acrobat Pro may restore these plug-ins too.
Hope that helps.